My fortress is currently under siege by some goblins and some trolls. The trolls obligingly rushed my trap maze, although sadly they all got caged before they reached the goblin grinders. Anyway, I'm getting ready to have some fun with them, but the two goblin squads are just sitting outside doing nothing, or having tea maybe, whether the doors to my fort are open or closed. This happened on the last siege too, and I lost a lot of civilians because the goblins wouldn't come politely to be killed. If it matters, the only way into my fort is through the traps, which previous goblins have "encountered".

I had the opposite problem on my previous fort, where goblins routinely charged in. However, if I remember correctly, that one had a non-trapped entrance which I could seal off with a bridge.

So: are the goblins not rushing in because their only routes are through traps? Or is there something else I should be doing?

2 Answers
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Goblins normally follow their squad captain, if he is alive, unless there's a dwarf within about 20 squares. Squad captains normally charge your base if they can find a path, trapped or not, to a dwarf, and their squads follow. (Note: the previous answer is incorrect; goblins are just as omniscient as you are, except they can't see traps.) However, a known bug right now is that goblins with flying mounts sometimes get confused and have a hard time pathing; this especially affects captains because they're mounted more often than the normal troops. If the captain's mount is confused, his squaddies will just stand around guarding him, rather than attacking on their own. This is similar to the problem that causes attackers to hang around your entrance rather than heading farther in: their captain is caught in a cage trap, but he's not dead so they just stand around rather than leaving him behind.

How to diagnose this: First, find the goblin captain on the units screen. He's the one marked "Elite" or "Master", and he'll probably have a different weapon from his squaddies. Zoom to the creature, and see if he's inexplicably floating above the world, especially if he's above a tree or something. If so, you'll have to order the militia out there, because that's the only way you're going to get rid of them; and you'll have to gain some height so that your marksdwarves can shoot at the captain, remembering that they can't shoot upward. You might have to build a small tower nearby to arrange this. An goblin master bowman stuck atop a tree with no higher ground nearby is a deadly threat, almost impossible to get rid of, because he shoots any of your masons who try to build a tower for the marksdwarves to stand on (and master bowmen are ridiculously dangerous).

If the captain's just parked on the ground, with his buddies, and not attacking you, something else is wrong: probably there isn't actually any way into your fortress. Check the doors; besieging goblins won't path through locked doors or raised drawbridges. Trolls path TO these obstacles because they're building destroyers and they like to destroy them, but goblins care only for dwarves. So go ahead and open the gates. Just make sure the militia is standing behind, and your civilians are burrow-restricted not to go outside, &c.

Yes! All of the goblins are on Giant Bats! And in the last siege the leader was on one! Well done indeed.
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andronikusNov 16 '11 at 21:45

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It's too bad this is a bug, because it's actually a good strategy. By not rushing in, they force me to either let my civilians out (to eventually be killed), deploy my military (which is basically my last line of defense), or try to lure them back to my traps. Incidentally, here's the bug tracker page about the mount bug: bay12games.com/dwarves/mantisbt/print_bug_page.php?bug_id=3015
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andronikusNov 17 '11 at 20:04

Yeah... In an upcoming version (possibly not this next one, but sometime "soon", invaders will actually do this intentionally: if they've had bad experiences with a particular entrance before (and someone escaped to tell the general about it), they'll try to find another one, or dig a new entrance if they know all the ones they can find are deathtraps. This will make basic fortress defense MUCH more exciting; trolls can be extremely fast miners, much faster than all but the most skilled dwarves.
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Paul ZNov 17 '11 at 22:55

They'll be able to dig? Sweet Armok's platelets! That will be exciting/terrifying.
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andronikusNov 18 '11 at 1:24

OK, well the obvious defense against digging goblins is surrounding the fort with a spherical lava moat. Or boring old water, but that involves less lava.
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andronikusNov 18 '11 at 17:01

No, goblins cannot see traps, but, if you lock your door when they come, they'll realize that they can't get to you and stop trying, even if you unlock the door. They'll just hang around until they see something to kill. To get them to try again, you usually have to let them chase a dwarf through said door. If you get them to see a dwarf on the other side of a line of traps, they should charge him, your dwarf should run away, and you should have some new play-things.

An easy way to do this is to send a single military dwarf out of your door, so that they can see him, and then demilitarize him, so he'll run back. A less risky way is to try to get a useless animal to wander out, but these methods don't work very well at all in open spaces, as the dwarf/cat just runs away, not to safety.

You might also have some luck in an open area by keeping the dwarf in the military and telling him to move back, but I think they'll usually just fight the goblins and get themselves killed.

Yeah, my civilian dwarves pretty much run in any direction but back to the fort. Dang, and here I thought I was all clever putting my fort entrance in the hollow of a cliff! Thanks!
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andronikusNov 16 '11 at 20:34

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Adding the bait dwarf to a burrow when he has attracted the goblins should not only return the dwarf to safety, but also draw the goblins right into the traps
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HackworthNov 16 '11 at 21:17

Goblins won't only attack your dwarves on sight, but also your pet animals. So if you don't want to risk a dwarv create a one by one zone in sight of the Goblins and assign a dog or cat to it.
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XenoxNov 16 '11 at 21:29

@Xenox: I said that in the second paragraph, but assigning will risk a dwarf anyway, since he'll have to drag the animal out there. Also, one that's a pet would make a poor dwarf sad. :(
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UllallullooNov 16 '11 at 21:38